1. Field of Invention
The present invention relates to airborne systems, and particularly to hyperspectral scanning systems incorporating relays.
2. Brief Description of the Related Art
Significant advances have been accomplished in the development of airborne hyperspectral systems. The hyperspectral sensor is a major part of airborne surveillance systems. The airborne sensor requires high performance optics that provides broad spectral coverage on over a deployed field of view (FOV). High spectral and spatial resolution also is required to detect and recognize ground targets from high altitude.
Typical airborne hyperspectral optical system consists of fore-optics, relay (or reimaging optical system) and spectrometer.
U.S. Pat. No. 6,886,953 (May 3, 2005) discloses imaging all-reflective spectrometer which consists of objective module in a form of three mirror anastigmat (TMA) or in a form of five powered mirrors and collimating-and-imaging module which comprises a set of three powered mirrors. The intermediate image is created between the objective module secondary and tertiary mirrors and intermediate pupil is created before the collimating-and-imaging module entrance slit. System includes imaging detector which receives a portion of the objective module output, and a hyper-spectral imaging detector that receives a portion of the output of the collimating-and-imaging module. There is no telecentric pattern of light at the intermediate pupil plane and cross field scanning cannot be implemented.
U.S. Pat. No. 5,880,834 (Mar. 9, 1999) discloses an imaging system having all-reflective fore-optics in the form of TMA, and an imaging Offner spectrometer. The fore-optics forms an intermediate image at a slit before the spectrometer. An off-axis primary spectrometer mirror delivers radiation onto a secondary spectrometer mirror/diffraction grating, and a tertiary spectrometer mirror reflects light from the grating to form multi-spectral images on a detector surface.
Further. U.S. Pat. No. 6,100,974 (Aug. 8, 2000) discloses an imaging all-reflective system including fore-optics also in the form of a TMA, and a dispersive Offner spectrometer consisting of three mirrors decentered with respect to one another. All relevant portions of the mentioned >834 and >974 U.S. patents are incorporated by reference.
Further, U.S. Pat. No. 7,944,559 (May 17, 2011) discloses airborne all-reflective hyperspectral imaging system with a fore-optics and Offner type spectrometer having one common axis of symmetry.
There are drawbacks of known hyperspectral imaging systems deployed in airborne and military applications, however. Existing hyperspectral imaging systems are not compact and cannot be deployed for scanning the target on the existing platforms.
Accordingly, there is a need for a high performance hyperspectral scanning imaging airborne system that is compact and provides good performance across the field and spectrum.